<s>
VMAC	B-Algorithm
is	O
a	O
block	O
cipher-based	O
message	B-Algorithm
authentication	I-Algorithm
code	I-Algorithm
(	O
MAC	O
)	O
algorithm	O
using	O
a	O
universal	B-Algorithm
hash	I-Algorithm
proposed	O
by	O
Ted	O
Krovetz	O
and	O
Wei	O
Dai	O
in	O
April	O
2007	O
.	O
</s>
<s>
VMAC	B-Algorithm
is	O
designed	O
to	O
have	O
exceptional	O
performance	O
in	O
software	O
on	O
64-bit	O
CPU	O
architectures	O
while	O
still	O
performing	O
well	O
on	O
32-bit	O
architectures	O
.	O
</s>
<s>
A	O
closely	O
related	O
variant	O
of	O
VMAC	B-Algorithm
that	O
is	O
optimized	O
for	O
32-bit	O
architectures	O
is	O
given	O
by	O
UMAC	B-Algorithm
.	O
</s>
<s>
VMAC	B-Algorithm
is	O
a	O
MAC	O
in	O
the	O
style	O
of	O
Wegman	O
and	O
Carter	O
.	O
</s>
<s>
This	O
short	O
string	O
is	O
then	O
combined	O
by	O
addition	O
with	O
a	O
pseudorandom	O
pad	O
,	O
resulting	O
in	O
the	O
VMAC	B-Algorithm
tag	O
.	O
</s>
<s>
The	O
nonce	O
need	O
not	O
be	O
kept	O
secret	O
,	O
but	O
care	O
needs	O
to	O
be	O
taken	O
to	O
ensure	O
that	O
,	O
over	O
the	O
lifetime	O
of	O
a	O
VMAC	B-Algorithm
key	O
,	O
a	O
different	O
nonce	O
is	O
used	O
with	O
each	O
message	O
.	O
</s>
<s>
VMAC	B-Algorithm
uses	O
a	O
function	O
,	O
called	O
VHASH	O
(	O
also	O
specified	O
in	O
this	O
document	O
)	O
,	O
as	O
the	O
keyed	B-Algorithm
hash	I-Algorithm
function	I-Algorithm
H	O
and	O
uses	O
a	O
pseudorandom	O
function	O
F	O
whose	O
default	O
implementation	O
uses	O
the	O
AES	O
block	O
cipher	O
.	O
</s>
<s>
VMAC	B-Algorithm
allows	O
for	O
tag	O
lengths	O
of	O
any	O
64-bit	O
multiple	O
up	O
to	O
the	O
block	O
size	O
of	O
the	O
block	O
cipher	O
in	O
use	O
.	O
</s>
<s>
When	O
using	O
AES	O
,	O
this	O
means	O
VMAC	B-Algorithm
can	O
produce	O
64	O
-	O
or	O
128-bit	O
tags	O
.	O
</s>
<s>
The	O
theory	O
of	O
Wegman-Carter	O
MACs	O
and	O
the	O
analysis	O
of	O
VMAC	B-Algorithm
show	O
that	O
if	O
one	O
"	O
instantiates	O
"	O
VMAC	B-Algorithm
with	O
truly	O
random	O
keys	O
and	O
pads	O
then	O
the	O
probability	O
that	O
an	O
attacker	O
(	O
even	O
a	O
computationally	O
unbounded	O
one	O
)	O
produces	O
a	O
correct	O
tag	O
for	O
messages	O
of	O
its	O
choosing	O
is	O
less	O
than	O
1/260	O
or	O
1/2120	O
when	O
the	O
tags	O
are	O
of	O
length	O
64	O
or	O
128	O
bits	O
,	O
respectively	O
.	O
</s>
<s>
In	O
an	O
applied	O
implementation	O
of	O
VMAC	B-Algorithm
,	O
using	O
AES	O
to	O
produce	O
keys	O
and	O
pads	O
,	O
these	O
forgery	O
probabilities	O
increase	O
by	O
a	O
small	O
amount	O
related	O
to	O
the	O
security	O
of	O
AES	O
.	O
</s>
<s>
Analysis	O
of	O
VMAC	B-Algorithm
security	O
has	O
been	O
carried	O
out	O
by	O
authors	O
Wei	O
Dai	O
and	O
Ted	O
Krovetz	O
.	O
</s>
